Improved kinetics of nanoparticle-decorated Mg-Ti-Zr nanocomposite for hydrogen storage at moderate temperatures

Abstract

The hydrogenation kinetics of Mg can be improved by mixing with Ti hydrides catalytic additives. But the dehydrogenation kinetics of Mg is still not acceptable in the practical application cases. To address this dilemma, Zr hydride is introduced into the Mg-Ti system. The Mg-TiH1.971-TiH1.5-ZrH1.66 nanocomposite is synthesized by hydrogen plasma-metal reaction (HPMR) method and activation process at 673 K. The synthesized nanocomposite presents the special surficial decorated nanostructure, that is the surfaces of Mg nanoparticles (NPs) of about 130 nm are uniformly embedded with the spherical TiH1.971-TiH1.5-ZrH1.66 NPs (20 nm). It is demonstrated that the decorated TiH1.971-TiH1.5-ZrH1.66 NPs can act as a combining catalytic effect in improving the hydrogen sorption kinetics of Mg at moderate temperatures. The decorated TiH1.971-TiH1.5-ZrH1.66 NPs has a pioneer (de)hydrogenation effect, causing the H concentration difference from the surface and inner core of Mg, favorably for the following hydrogen sorption of Mg. Particularly, the dehydrogenation kinetics is significantly enhanced as the result of the introduction of Zr hydride NPs. The Mg-TiH1.971-TiH1.5-ZrH1.66 nanocomposite can efficiently uptake 4.2 wt % H2 within 5 min at 473 K and 3.0 wt % H2 in 5 min at 373 K, and release hydrogen at 573 K and reach a value of 2.7 wt % in 5 min. Even at 473 K the Mg-TiH1.971-TiH1.5-ZrH1.66 nanocomposite can quickly release 1.0 wt % H2 in 10 min.